The use of oil-based muds and drilling fluids has become increasingly popular since their introduction of the technology in the 1950's. Innovations in oil-based muds and drilling fluids are of on-going importance with the development of environmentally friendly drilling fluids and fluids having other special characteristics. Oil-based muds offer advantages over water-based muds in many drilling situations. In particular, oil-based muds are known in the art to provide excellent shale inhibition, borehole stability, lubricity, thermal stability, corrosion inhibition, tolerance of contamination and ease of maintenance. The selection of an oil-based drilling fluid, also known as oil-based mud involves a careful balance of both good and bad characteristics of such fluids in a particular application and the type of the oil or gas field in which the well is to be drilled.
Invert emulsion fluids or drilling muds are often utilized during the drilling of a subterranean well with an oil-based drilling fluid. Invert emulsion fluids generally include three major components, namely an oleaginous liquid which serves as a continuous phase, a non-oleaginous liquid which serves as a discontinuous phase and an emulsifying agent.
In addition to these three principle ingredients, lime or other alkaline materials are added to conventional invert emulsion fluids to maintain an alkaline reserve. The alkaline reserve is critical to maintaining the emulsion stability and the rheology of the conventional oil-based drilling fluid and thus the fluids usefulness in drilling. In some oil field areas, acidic gases such as CO.sub.2 or H.sub.2 S may be present in the formations penetrated by the well. These acidic gases can destabilize the invert emulsion causing the formation of a "flip-mud" which causes the immediate shut-down of drilling rig operations. The removal of flip mud from the well is costly and time consuming because the mud has a high viscosity. One of skill in the art should know that once a "flip-mud" has formed the invert emulsion fluid is considered to be useless and the components must be disposed of at great expense. Thus the role of the alkaline reserve, typically in the form of lime, is critical to prevent the formation of "flip-mud" and the accompanying instability and viscosity problems caused by acidic gases.
Although the inclusion of an alkaline reserve in the formulation of oil-based drilling fluids and invert emulsion is beneficial, sometimes it is desirable to log the amount of the acidic gases encountered during the drilling operation. The presence of the alkaline reserve inhibits the logging of acidic gases, in particular CO.sub.2 and H.sub.2 S, because of the rapid acid/base reaction that takes place. Thus it would be desirable and useful if one could formulate an oil-based drilling fluid without use of lime or other alkaline reserve materials. In this way since the oil-based drilling fluid will not react with acidic gases, it could be utilized in fields in which acidic gas containing formations are known or suspected. This will allow the drill rig operator to accurately analyze the gases present in the mud by suitable means such as gas chromatography, gas sensitive probes or titration of such acidic gases as CO.sub.2 and H.sub.2 S.